1. Technical Field
The present invention relates to a method of receiving a satellite signal which carries a navigation message therewith, and the like.
2. Related Art
As a positioning system using a positioning signal, GPS (Global Positioning System) is widely known and has been adopted in a receiving apparatus which is built into a mobile phone, a car navigator, and the like. GPS obtains the positions of a plurality of GPS satellites, a pseudo distance from each of the GPS satellites to the receiving apparatus, and the like using the measured time of a GPS receiver and finally calculates the position thereof.
The GPS satellite transmits information on satellite orbits, times, and the like including navigation messages at a bit rate of 50 bps (bits per second). A single navigation message is configured of one master frame, and the one master frame is configured of 25 frames, each of which is configured of 1500 bits. In order to acquire all of the navigation messages, it is necessary to receive 25 frames configuring the master frame, which takes 12.5 minutes.
The environment in which the GPS satellite signal is received varies depending on the position of the receiving apparatus, and the like. In an environment with a weak electric field, the signal intensity of the received signal is weak. Accordingly, the variation (bit transition) in a bit value of the navigation message cannot be accurately detected and thus there is a possibility that an error may occur in demodulating the received signal. Therefore, a technique determining whether or not the demodulation of the received signal is correct is disclosed (for example, refer to JP-T-2008-541629).
JP-T-2008-541629 discloses an error detection which performs an inspection for each word included in each subframe of the navigation message in accordance with a previously regulated operational equation using a parity bit of six bits stored at the end of the word. However, it is inefficient that the received data is discarded due to a demodulation error in one bit. In such a case, a lot of time is needed to collect parameters which are required to calculate the satellite orbits. Therefore, there is a problem in that the Time to First Fix (TTFF) increases.